Abstract: he transfer of 131I to sheep milk was measured in a controlled feeding experiment using herbage recently contaminated by fallout from the Chernobyl accident. The transfer coefficient (fm) of131I from the Chernobyl-contaminated herbage was 0·29±0·017 day litre−1. The daily proportion of 131I intake which was secreted in milk was 56±0·035%. This is an order of magnitude higher than for cattle and agrees with the higher transfer of stable iodine from plasma to milk which occurs in sheep and goats.